IMPLEMENTATION MODULE CRC;
(*
 *  REPERTOIRE
 *  Release 1.6
 *  By Charles Bradford and Cole Brecheen
 *  (c) Copyright 1985-1992 PMI
 *  Green Bay, Wisconsin
 *  All rights reserved
 *  (414) 468-6040
 *
 *  $Header:   D:/logfiles/mods/crc.mov   1.5   10 Mar 1991 15:25:48   coleb  $
 *
 *
 *  Written and contributed by David Tingler of
 *  Telepath Systems, Inc., in Norman, Oklahoma.
 *
 **** JDM October 3, 1989 fix (I hope) bug in AddCRC
 **** JDM/MBC March 21, 1990.  Add CalcCRCChain to permit multiple buffers
 ****   to be processed with successive calls.
 *)


IMPORT LowLevel;
IMPORT SYSTEM;

VAR
  Initialized : BOOLEAN;

VAR
  crctab: ARRAY [0..255] OF BITSET;

(*$S-*)
(*$R-*)
(*$T-*)

PROCEDURE CalcCRCChain
          (    lastCRC : CARDINAL;     (* in - 0 first time, last otherwise *)
               BufAdr: SYSTEM.ADDRESS;
               BufSize: CARDINAL
          ): CARDINAL;
  VAR
    segm, offs, h, i: CARDINAL;
  BEGIN
    i := 0;
    h := BufSize - 1;
    segm := LowLevel.seg( BufAdr );
    offs := LowLevel.ofs( BufAdr );
    FOR i := 0 TO h DO
      AddCRC(lastCRC, LowLevel.PeekByte(segm, offs + i));
    END;
    RETURN lastCRC;
  END CalcCRCChain;
(**** end of "new" procedure.  *)


PROCEDURE CalcCRC( BufAdr: SYSTEM.ADDRESS; BufSize: CARDINAL ): CARDINAL;
  VAR
    segm, offs, h, i, crc: CARDINAL;
  BEGIN
    crc := 0;
    i := 0;
    h := BufSize - 1;
    segm := LowLevel.seg( BufAdr );
    offs := LowLevel.ofs( BufAdr );
    FOR i := 0 TO h DO
      AddCRC(crc, LowLevel.PeekByte(segm, offs + i));
    END;
    RETURN crc;
  END CalcCRC;


PROCEDURE AddCRC(VAR crc: CARDINAL; ch: SYSTEM.BYTE);
  VAR
    CRC, c: BITSET;
    tab: CARDINAL;
  BEGIN
    c   := BITSET( ORD(ch) );
    CRC := BITSET( crc );
    tab := CARDINAL( (CRC / c) * {0..7} );
      (* (crc XOR c) AND 0FFH *)
(*  CRC := (BITSET(CARDINAL(CRC) * 256) * {0..7}) / crctab[tab]; *)
    CRC := BITSET(CARDINAL(CRC) DIV 256) / crctab[tab];
      (* SHIFT(crc, 8)  XOR crctab[tab] *)
    crc := CARDINAL(CRC);
  END AddCRC;


VAR i: CARDINAL;

PROCEDURE InitNum(x: CARDINAL);
  BEGIN
    crctab[i] := BITSET(x);
    INC(i);
  END InitNum;


  PROCEDURE Init();
    BEGIN
      IF Initialized THEN
        RETURN;
      ELSE
        Initialized := TRUE;
      END;
      LowLevel.Init();

      i := 0;
      InitNum(00000H); InitNum(0C0C1H); InitNum(0C181H); InitNum(00140H);
      InitNum(0C301H); InitNum(003C0H); InitNum(00280H); InitNum(0C241H);
      InitNum(0C601H); InitNum(006C0H); InitNum(00780H); InitNum(0C741H);
      InitNum(00500H); InitNum(0C5C1H); InitNum(0C481H); InitNum(00440H);
      InitNum(0CC01H); InitNum(00CC0H); InitNum(00D80H); InitNum(0CD41H);
      InitNum(00F00H); InitNum(0CFC1H); InitNum(0CE81H); InitNum(00E40H);
      InitNum(00A00H); InitNum(0CAC1H); InitNum(0CB81H); InitNum(00B40H);
      InitNum(0C901H); InitNum(009C0H); InitNum(00880H); InitNum(0C841H);
      InitNum(0D801H); InitNum(018C0H); InitNum(01980H); InitNum(0D941H);
      InitNum(01B00H); InitNum(0DBC1H); InitNum(0DA81H); InitNum(01A40H);
      InitNum(01E00H); InitNum(0DEC1H); InitNum(0DF81H); InitNum(01F40H);
      InitNum(0DD01H); InitNum(01DC0H); InitNum(01C80H); InitNum(0DC41H);
      InitNum(01400H); InitNum(0D4C1H); InitNum(0D581H); InitNum(01540H);
      InitNum(0D701H); InitNum(017C0H); InitNum(01680H); InitNum(0D641H);
      InitNum(0D201H); InitNum(012C0H); InitNum(01380H); InitNum(0D341H);
      InitNum(01100H); InitNum(0D1C1H); InitNum(0D081H); InitNum(01040H);
      InitNum(0F001H); InitNum(030C0H); InitNum(03180H); InitNum(0F141H);
      InitNum(03300H); InitNum(0F3C1H); InitNum(0F281H); InitNum(03240H);
      InitNum(03600H); InitNum(0F6C1H); InitNum(0F781H); InitNum(03740H);
      InitNum(0F501H); InitNum(035C0H); InitNum(03480H); InitNum(0F441H);
      InitNum(03C00H); InitNum(0FCC1H); InitNum(0FD81H); InitNum(03D40H);
      InitNum(0FF01H); InitNum(03FC0H); InitNum(03E80H); InitNum(0FE41H);
      InitNum(0FA01H); InitNum(03AC0H); InitNum(03B80H); InitNum(0FB41H);
      InitNum(03900H); InitNum(0F9C1H); InitNum(0F881H); InitNum(03840H);
      InitNum(02800H); InitNum(0E8C1H); InitNum(0E981H); InitNum(02940H);
      InitNum(0EB01H); InitNum(02BC0H); InitNum(02A80H); InitNum(0EA41H);
      InitNum(0EE01H); InitNum(02EC0H); InitNum(02F80H); InitNum(0EF41H);
      InitNum(02D00H); InitNum(0EDC1H); InitNum(0EC81H); InitNum(02C40H);
      InitNum(0E401H); InitNum(024C0H); InitNum(02580H); InitNum(0E541H);
      InitNum(02700H); InitNum(0E7C1H); InitNum(0E681H); InitNum(02640H);
      InitNum(02200H); InitNum(0E2C1H); InitNum(0E381H); InitNum(02340H);
      InitNum(0E101H); InitNum(021C0H); InitNum(02080H); InitNum(0E041H);
      InitNum(0A001H); InitNum(060C0H); InitNum(06180H); InitNum(0A141H);
      InitNum(06300H); InitNum(0A3C1H); InitNum(0A281H); InitNum(06240H);
      InitNum(06600H); InitNum(0A6C1H); InitNum(0A781H); InitNum(06740H);
      InitNum(0A501H); InitNum(065C0H); InitNum(06480H); InitNum(0A441H);
      InitNum(06C00H); InitNum(0ACC1H); InitNum(0AD81H); InitNum(06D40H);
      InitNum(0AF01H); InitNum(06FC0H); InitNum(06E80H); InitNum(0AE41H);
      InitNum(0AA01H); InitNum(06AC0H); InitNum(06B80H); InitNum(0AB41H);
      InitNum(06900H); InitNum(0A9C1H); InitNum(0A881H); InitNum(06840H);
      InitNum(07800H); InitNum(0B8C1H); InitNum(0B981H); InitNum(07940H);
      InitNum(0BB01H); InitNum(07BC0H); InitNum(07A80H); InitNum(0BA41H);
      InitNum(0BE01H); InitNum(07EC0H); InitNum(07F80H); InitNum(0BF41H);
      InitNum(07D00H); InitNum(0BDC1H); InitNum(0BC81H); InitNum(07C40H);
      InitNum(0B401H); InitNum(074C0H); InitNum(07580H); InitNum(0B541H);
      InitNum(07700H); InitNum(0B7C1H); InitNum(0B681H); InitNum(07640H);
      InitNum(07200H); InitNum(0B2C1H); InitNum(0B381H); InitNum(07340H);
      InitNum(0B101H); InitNum(071C0H); InitNum(07080H); InitNum(0B041H);
      InitNum(05000H); InitNum(090C1H); InitNum(09181H); InitNum(05140H);
      InitNum(09301H); InitNum(053C0H); InitNum(05280H); InitNum(09241H);
      InitNum(09601H); InitNum(056C0H); InitNum(05780H); InitNum(09741H);
      InitNum(05500H); InitNum(095C1H); InitNum(09481H); InitNum(05440H);
      InitNum(09C01H); InitNum(05CC0H); InitNum(05D80H); InitNum(09D41H);
      InitNum(05F00H); InitNum(09FC1H); InitNum(09E81H); InitNum(05E40H);
      InitNum(05A00H); InitNum(09AC1H); InitNum(09B81H); InitNum(05B40H);
      InitNum(09901H); InitNum(059C0H); InitNum(05880H); InitNum(09841H);
      InitNum(08801H); InitNum(048C0H); InitNum(04980H); InitNum(08941H);
      InitNum(04B00H); InitNum(08BC1H); InitNum(08A81H); InitNum(04A40H);
      InitNum(04E00H); InitNum(08EC1H); InitNum(08F81H); InitNum(04F40H);
      InitNum(08D01H); InitNum(04DC0H); InitNum(04C80H); InitNum(08C41H);
      InitNum(04400H); InitNum(084C1H); InitNum(08581H); InitNum(04540H);
      InitNum(08701H); InitNum(047C0H); InitNum(04680H); InitNum(08641H);
      InitNum(08201H); InitNum(042C0H); InitNum(04380H); InitNum(08341H);
      InitNum(04100H); InitNum(081C1H); InitNum(08081H); InitNum(04040H);
    END Init;

BEGIN
  Initialized := FALSE;
  Init();
END CRC.